1. Field of the Invention
The invention relates to the field of providing a synthesis technique to grow bulk quantities of semiconductor nanowires at temperatures less than 500xc2x0 C.
2. Description of the Prior Art
One-dimensional semiconductor fibers are useful for many applications ranging from probe microscopy tips to interconnections in nanoelectronics. By xe2x80x9cone-dimensionalxe2x80x9d it is meant that the fibers have extremely small diameters, approaching 40 xc3x85ngstroms. The fibers may be termed xe2x80x9cnanowiresxe2x80x9d or xe2x80x9cwhiskers.xe2x80x9d Several methods are known for synthesis of these fibers. Included are VLS (vapor-liquid-solid) growth, laser ablation of silicon and silicon oxide species and combinations of these techniques.
In VLS growth, a liquid metal cluster or catalyst acts as the energetically favored site of absorption of gas-phase reactants. The cluster supersaturates and grows a one-dimensional structure of the material. A VLS method has been used to grow silicon nanowires by absorption of silane vapor on a gold metal surface. Variations of this methods have been used to produce other semiconductor fibers.
One variation is laser ablation. In this technique, the silicone species, such as SiO2, is ablated to the vapor phase by laser excitation.
The present invention provides a method of synthesizing semiconductor fibers by placement of gallium or indium metal on a desired substrate, placing the combination in a low pressure chamber at a vacuum from 100 mTorr to one atmosphere pressure in an atmosphere containing desired gaseous reactants, raising the temperature of the metal to a few degrees above its melting point by microwave excitation, whereby the reactants form fibers of the desired length. When the metal is gallium, a temperature of about at least 50xc2x0 C. is sufficient, preferably near 300xc2x0 C. for best solubility and mobility within the melt. When the metal is indium, a temperature of about 200xc2x0 C. is preferred. Preferably the substrate is silicon, most preferably silicon comprising an electronically useful pattern; the metal is gallium, the gaseous reactant is hydrogen, and the fibers formed comprise SiHx. The gallium metal may be applied either in solid or droplet form or in the form of patterned droplets for patterning silicon microwires. Other forms of gallium droplet patterns may also include droplets in two dimensional and three dimensional channels for directed growth.
Another preferable substrate is germanium with hydrogen as gaseous reactant. The reactant hydrogen will form germane, GeHx in the gas phase which upon decomposition on a gallium substrate results in the deposition of germanium into gallium droplets. The dissolved germanium grows out as germanium nanowires.
Other semiconductors materials may be synthesized according to the methods of this invention. In each case, gallium or indium metal is used as the absorption sit-catalyst. Where the substrate is not readily vaporized to provide a gaseous reactant, a vapor substrate will be added to the reactive atmosphere. For example, GaAs substrates may be used, with a gallium drop and nitrogen in the gas phase, to grow GaN nanofibers.
These and other objects of the present invention will be more fully understood from the following description of the invention.